THE NBBVOUS SYSTEM 309
magnus except the strip going to the internal condyle of the femur. The chief variation among the Apes is the presence or absence of the twig to the pectineus; when it is present the pectineus includes part of the adductor longus.
The superior gluteal nerve arises in the Gibbons alone from the lumbo-sacral cord. In other Apes it springs from sacral nerves. Its course and distribution are as in Man, with the addition of a twig to the scansorius. The inferior gluteal nerve is as in Man ; and the small sciatic nerve ends in the skin of the calf.
The great sciatic nerve in the Chimpanzee emerges from the pelvis, winds round the ischial tuberosity and enters the back of the thigh. It divides at any point between the tuber ischii and popliteal space into the external and internal popliteal nerves. The former breaks up into anterior tibial and musculo-cutaneous nerves, and the latter becomes the posterior tibial nerve. In the Chimpanzee it first supplies the obturator in-ternus, gemelli, quadratus femoris, biceps and gluteus maximus ; and it supplies the hamstring muscles in the thigh. The external popliteal nerve supplies the biceps, extensor longus digitorum and knee-joint. Its continuation, the anterior tibial nerve, supplies the anterior tibial muscles, flexor brevis digitorum, ankle and tarso-meta-tarsal joints and the skin of the adjacent sides of the hallux and index. Ths musculo-cutaneous nerve supplies only the skin of the adjacent sides of the index, medius, annularis and minimus. No sural nerve exists. The posterior tibial nerve supplies both heads of the gastro-
cnemius, anterior tibial, posterior tibial and «peroneal